Abstract
Background
The gradual conversion of rangelands into other land use types is one of the main challenges affecting the sustainable management of rangelands in Teltele. This study aimed to examine the changes, drivers, trends in land use and land cover (LULC), to determine the link between the Normalized Difference Vegetation Index (NDVI) and forage biomass and the associated impacts of forage biomass production dynamics on the Teltele rangelands in Southern Ethiopia. A Combination of remote sensing data, field interviews, discussion and observations data were used to examine the dynamics of LULC between 1992 and 2019 and forage biomass production.
Results
The result indicate that there is a marked increase in farm land (35.3%), bare land (13.8%) and shrub land (4.8%), while the reduction found in grass land (54.5%), wet land (69.3%) and forest land (10.5%). The larger change in land observed in both grassland and wetland part was observed during the period from 1995–2000 and 2015–2019, this is due to climate change impact (El-Niño) happened in Teltele rangeland during the year 1999 and 2016 respectively. The quantity of forage in different land use/cover types, grass land had the highest average amount of forage biomass of 2092.3 kg/ha, followed by wetland with 1231 kg/ha, forest land with 1191.3 kg/ha, shrub land with 180 kg/ha, agricultural land with 139.5 kg/ha and bare land with 58.1 kg/ha.
Conclusions
The significant linkage observed between NDVI and LULC change types (when a high NDVI value, the LULC changes also shows positive value or an increasing trend). In addition, NDVI value directly related to the greenness status of vegetation occurred on each LULC change types and its value directly linkage forage biomass production pattern with grassland land use types. 64.8% (grass land), 43.3% (agricultural land), 75.1% (forest land), 50.6% (shrub land), 80.5% (bare land) and 75.5% (wet land) more or higher dry biomass production in the wet season compared to the dry season.
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Background
Rangeland management is a principle involved in regulating and assessing the vegetation, soil, forage production and livestock distribution status [1]. Rangelands represent a key source of pasture for livestock production and covered most of the arid and semi-arid environmental region of Ethiopia [2]. Rangeland vegetation coverage and forage production is determined by both physical (climate, topography and soil) biological (like grazing) and anthropogenic factors [3,4,5]. The rangelands in Ethiopia including Teltele are rainfall dependent and frequently exposed to irregular rainfall pattern and drought [6]. In addition, this variability has been considered one of the primaries that determined the rangeland forage production [7, 8]. In Teltele, pastoralists rangeland serves as the major economic source [9]. Currently, it is highly vulnerable to the impact of climate change like bush encroachment, drought and the expansion of farming practice that causes decline of forage production and quality [10, 11]. In semi-arid and arid rangeland, climate change and variability determine the structure and function of rangeland vegetation relative to other factors like grazing intensity [12, 13]. The rangeland vegetation status and the forage production also varying spatially with soil characteristics and topography [14]. In Ethiopia, rangelands are lost due to changes in land use system like dramatic expansion of farming practices, establishment of private and government ranches, the rapid infestation of bush plant species and a major facilitator with climate change impact [15, 16]. The Teltele pastoralists typically have a traditional management practice applied to use and manage the resources of their rangeland for a long period of time [17].
However, nowadays, the trend become weakened and part of rangeland replaced by farming are being activated [18]. Managing rangelands requires a combination of biological, physical and social techniques [ Distributions of respondent’s demographic characteristics. M male, F female, TE tertiary education, HS high school, PE primary school, NE not educated, LR livestock rearing, E employment, B business, L labor work, NW Not known work
Driver of change of vegetation land cover and forage biomass
According to the data obtained from group discussion and interviews, the major drivers which influenced the change in land use-land cover and forage biomass production dynamics in Teltele rangeland, the bush infestation ranked as the primary reason (25.8%), followed by drought (20%) and expansion of agricultural practice (15%), increment of the population both human and livestock in the district (12.5%) without additional land provided (Table 3). Government policies have also had their own impact on the livelihoods of pastoralists, in Teltele, which promote the transformation of rangeland into cultivated land and restrict the movement of pastoralists who were traditionally used to co** with the impact of climate change. And also, existence of different insects that eat and damage the forage species (6.7%) and poor pastoralist interaction are also another driving force for change of land use/cover and also forging biomass product in the study area.
Discussion
In Teltele the grassland, natural forest and wetland mainly change into agricultural land at an alarming rate. This is due to the factors such as government's current land policies, rapid infestation of bush plant species, climatic and anthropogenic factors. The current land government policies which encouraged the pastoral community to participate in agricultural practice in addition to the scarcity of livestock, since the frequent climatic changes, like drought, challenges the livestock sector and as well as the livelihood of the pastoral community [9, 12]. Therefore, the government encourages the community to reduce their livestock and keep them around their home area by conserving some part of grazing area in the form of ranch and transforming the other part into agricultural [17]. This has caused the degradation of rangeland in the Teltele district. Bush encroachment is another major impacting factor in the study area. The infestation rate was high when the impact of climate change was harsh compared to the other period [32,33,34]. The most significant change in terrain observed in grassland and wetlands parts of Teltele rangeland occurred during the period from 1995–2000 and 2015–2019, this is due to climate change impact (El-Niño) that happened on the Teltele rangeland in 1999 and 2016 respectively (Figs. 1, 2; Table 1). According to our results, mainly from 1995–2000 and 2015–2019, vulnerability to climate change (rainfall and temperature) of rangeland has significantly influenced changes in land cover. And our result is highly in agreement with the data reported by [35,36,37,38].
The frequent decline of water source has a significant impact on the rangeland degradation and also on the livestock population on the rangeland area [34]. The shift of wetland to other land use types like agricultural and bush encroached areas results water scarcity on the grazing area and currently this is one of the major problems in the study area, that caused for the decline of the livestock number [16]. The transition matrices of LULC showed that major change was observed in grassland, wetland and forestland area and mainly transformed to agricultural land, bare land and shrub land LULC types (Table 2) from 2019 year, which is similar to the findings of [39]. As shown in (Fig. 3), the majority of grassland, wetland and forestland have decreased (negative change), whereas the agricultural land, bare land and shrub land have increased (positive change). This indicated that in 2019 (nowadays) the rangeland has degraded due to factors like expansion of farming practices, infestation of bush invasive species, and bare area expansion due to factors like flooding and high wind (climate change) in combination with different anthropogenic factors [40]. The major factors related to the growing challenges of maintaining a livestock-based livelihood system in the face of changing land use and recurring droughts [41]. However, Pastoralists in the study area are conscious of the potential threat of invasive plant species and often, the removal of most shrubs and trees not preferred by livestock on their rangeland had negative impact on the native grass species [35].
Rainfall is the main determinant factor for forage production in all land use type [36, 37]. When we have seen the amount of forage in different land use/cover types, the grasslands had the highest average amount of forage biomass of 2092.3 kg/ha followed by wetland with 1231 kg/ha, forest with 1,191.3 kg/ha, shrub land with 180 kg/ha, agricultural land with 139.5 kg/ha and bare land with 58.1 kg/ha (Fig. 4). This source of variation and dynamics of the forage biomass in the Teltele rangeland is due to a great influence of land use land cover change on the quantity of dry biomass recovered as well as the quantity of fresh weight forage in a given area. Further, the results showed that there was a significant interaction between the season and land cover types with forage biomass production dynamics in the study area and this result is in agreement with [38, 42]. From this we can understand that transition from grazing area (grassland) to other land use type had a significant impact on the reduction of forge biomass production and this was the current major problem on Teltele rangeland resulted to the decline of livestock and scarcity of income in the pastoralist livelihood. The expansion of agricultural land, bush land and bare land area have harmful effects on the forage production dynamics, but the expansion of agricultural land is more problematic in our study site, which is consistent with the data reported by [36, 43]. There is generally a link between the value of aboveground forage greenness (NDVI) and forage biomass and the linkage varied with the season and land use/cover types (Fig. 6). The forage biomass production showed a decline pattern from 1992 to 2019, according to the data obtained from the respondent (Table 5) and filed data (Fig. 4) due to the different driving factors and this is also directly related with the NDVI values. The significant linkage observed between NDVI and LULC changes, was used to estimate the forage biomass production trends across the rangeland compared to each LULC type [43,44,45]. This implies that there is a direct correlation between rainfall, vegetation greening and biomass production in Teltele rangeland [31]. If the rainfall was high, the vegetation cover of rangeland would be better as compared to the period when the rainfall was low or drought and from this, it can be understood that the greenery was also highly related with the losses of vegetation cover. Our result, directly in line with the data reported by [4]. The overall rangeland vegetation cover analysis and change detection showed remarkable grassland vegetation cover changes across the study site. The greatest change was the decrease in the grassland and wetland proportion of rangeland vegetation and the increase in the cropland and bush infested areas. In general, from the results of the focus group discussion interviews, we can understand that the introduction of privatized resources (enclosures) had caused shortages of communal grazing areas and limited animal mobility.
Thus, the situation affected the socio-economic structure and encouraged pastoralists to diversify their livelihoods with crop production because livestock had become uncertain, which causes the major factor in LULC change of grass land to agricultural land [4]. But there is still a big gap under the term of land use/cover change factors, rather the pastoral community liked that it was due to God's plan and to nature which could be intended to punish us. This was an indicator of community’s low awareness of the climate change with which the whole world is grappling with and our data are consisted with the data reported by [46]. In addition, undermining traditional land use practice also have a direct impact on LULC changes in Teltele [32,33,34]. Local communities claimed that traditional (customary) laws had become weak and that this has contributed to the observed LULC changes in the area. For example, rotation programs for seasonal grazing areas had been planned and maintained for the specified communities for extended periods [47]. In general, regarding to the Ethiopian's land-use policies and plans, a paper recently presented at the annual World Bank conference noted that because of a lack of a coherent policy use of land, the deterioration of land resources has been documented in the country [48, 49], which is similar to the opinions expressed by the respondents. For sustainable use of pastures in the district of Teltele, an awareness of the pastoral community on land use policies, respectful of the environment and regulating the growth of the human and animal population, was absolutely necessary.
Conclusions
This study focused on quantifying the status of land use and land cover classes and the forage biomass production of different land use types in Teltele rangeland. A large part of the changes in rangeland vegetation cover differ spatially across the study site. The main characteristics of the LULC changes observed in Teltele rangeland imply a reduction in the total amount of grassland, forestland and wetland, and a significant increase in agricultural, shrub and bare land area. As a result, the forage biomass production also showed great dynamics across each LULC during both wet and dry season. Grassland had the highest average amount of forage biomass of 2092.3 kg/ha, followed by wetland with 1231 kg/ha, forest land with 1191.3 kg/ha, shrub land with 180 kg/ha, agricultural land with 139.5 kg/ha and bare land with 58.1 kg/ha. From this, we can conclude that LULC was the main cause for forage biomass reduction in the Teltele rangeland area. The NDVI value for each LULC type and season showed a direct linkage with forge biomass production and the pattern of change in land use type either negative or loss and positive or gain. The NDVI value showed an increasing trend with land use type of agricultural land, shrub land and also forestland with value of 0.043 (6.8%), 0069 (9.9%) and 0.077(11.6%) respectively, whereas as in the land use type of grassland and wetland NDVI value showed a decreasing trend with value of 0.082 (15.2%) and 0.11(23.6%) respectively. Further, the NDVI value of Teltele rangeland highly related with the rainfall value. The forage biomass production in all LULC types was high, and this related to the greenery of the forage vegetation in the study area. Furthermore, with high NDVI value also high forage biomass production was observed, thus, NDVI and forage biomass have a direct linkage. Therefore, the sustainability of livestock grazing in the district will depend on the health of the grasslands for continuous mobile grazing practices to overcome the low amount of forage per hectare. The driving factors for the LULC changes in the Teltele rangeland area were the bush infestation, drought, expansion of agricultural practice, increment of the population both human and livestock, government policies and insects and disease were mentioned by the respondents. Therefore, land use and management techniques based on the interest of local communities and respectful of the eco-environmental are highly advised and recommended for wise and sustainable use of rangeland resource in the Teltele rangeland. Above all, the balance between the stoking rate with rangeland carrying capacity and balance of the livestock population used to reduce over degradation of the rangeland and the pursuit of awareness will be at the center of priorities.
Methods
Study area
The study was conducted at Teltele Woreda in the Borana zone of Southern Ethiopia (Fig. 8). The site was selected because it is one of the most arid parts of Borana zone and, therefore, the pastoral communities of this region are the most vulnerable to the rangeland degradation as a result of both human and climatic factors. It is located 666 km south of Addis Ababa, the capital city of Ethiopia. It lies approximately between 04° 56′ 23′ N latitude and 37° 41′ 51′ E longitude and the altitude are about 496–1500 m, the maximum altitude of 2059 m above sea level. The annual mean temperatures vary from 28 to 33 °C with little seasonal variation. The rainfall in the region is characterized as bi-modal. That is to say that 60% of rainfall occurs from March to May and 27% of rainfall occurs from September to November with high temporal and spatial fluctuations [50] (Fig. 9). The potential evapotranspiration is 700–3000 mm [51]. The soil in the study area includes, 53% red sandy loam soil, 30% black clay, and volcanic light-colored silt clay and 17% silt and the vegetation mainly dominated by encroaching woody species, and those that frequently thinned out, include Senegalia mellifera, Vachellia reficiens and Vachellia oerfota [40, 52]. According to the latest census conducted in 2015, the national census reported a total 70,501 of population for this woreda, of whom 36,246 men and 34,255 women; 4,874 or 6.91% of its population are urban dwellers. Cattle, goats, sheep, camel, mule, donkey and horse are the main livestock species reared.
Location map of the study area
Annual rainfall pattern of Teltele from 1992–2019 (Source: [53]). Max maximum, Min minimum
Data sources and methods
This study combined multispectral satellite remote sensing data, in-depth fieldwork surveys and rangeland use policy analysis linked with rangeland vegetation change source. The Teltele rangeland shape file along with weather data (rainfall and temperature) from 1992 to 2019 were obtained from [53] to see the long-term trend in the study site. To monitor the spatial and temporal conditions of rangeland vegetation, we used the annual average of third Generation Standard Difference Vegetation Index (NDVI3g) data (1992–2019). The model we used to extract data from the study area and remove the biased from our data in order to adopt land use land cover (LULC) analysis is summarized in (Fig. 10). The data derived from the Global Inventory Modeling and Map** Studies (GIMMS) with 8 km grid resolution. Before extracting the data to our study area, we resampled them to 300 m resolution of digital elevation model of Ethiopia in order to increase the resolution of the data. For NDVI grid cell values we simply took the maximum, minimum and an average annual mean value in order to reduce disturbance in the trends, such as those attributable to bare soil and sparsely vegetated areas [54, 55]. Vegetation maps of the Teltele district in 1992–2019 were obtained from the remote sensing data with spatial scale 1:100,000. The Landsat TM imageries acquired in 1992, 1995, 2000, 2005, 2010, 2015 and 2019 were used for range land vegetation cover classification and the characteristic of Landsat used for LULC change analysis was described at (Table 4). These years were chosen because of the availability of data, the quality of the images, and in order to compare the changes with in equal time intervals. Further, interviews and focal group discussions were conducted with the local pastoral community and stakeholders to verify the accuracy of the rangeland vegetation classified images analyzed by using ArcMap 10.3.1 software and furthermore, understand the possible major drivers and consequences of LULC changes in the rangeland. A total of 120 individuals (90 males and 30 females), 6 of them were stakeholders from different government sectors (4 males and 2 females) who have been lived 15 to 20 years in the study district, were selected, interviewed and discussed about the rangeland vegetation cover change and forage biomass production trend and as well as the major causes of change based on their observation and experience in the region. The priority driving factors for the changing of rangeland vegetation feature and biomass production were elaborated during the group discussions.
Schematic representation of the model used to extract data to the study area and their bias remove
The data pre-processing, clip** the area of interest (AOI) and applying color composites with different reflectance grids, were used to improve visualization and interpretation [56]. The general techniques we used LULC analysis was described in the form of chart below at (Fig. 11).
Methodological flow chart of the study
Classification of vegetation cover change
In order to clearly understand the change of rangeland vegetation cover, a post classification comparison detection technique was used by classification and detection of each pixel using the remote sensing map and compute the coverage of the area change [57]. The classes were classified based on the Intergovernmental Panel on Climate Change (IPCC) Classes considered for the change detection and Land Cover Classification System (LCCS) Legend used in the Climate Change Initiative Land Cover (CCI-LC) maps for the Images obtained from different years (Table 5).
The most widely used method for change detection is the comparative analysis of the spectral classification over a time series and filtered to reduce the poorly classified pixels [58, 59]. Each classified image was compared for the detection of vegetation cover change and the summaries of the areas and percentages of change were calculated.
Forage biomass production dynamics
In order to quantify the forage biomass dynamics in different land cover classes, above ground biomass measurement was conducted. A 5 km transect was lied and systematically placed six 25 × 25 m2 sampling plot at 500 m interval along a transect at each land class site. (in total 36 plots from the six land classes). In addition, within each plot three (3) 5 × 5m2 sub plots (in total 108) were placed. Finally, five (5) 1 × 1 m2 quadrants was placed by randomly throwing them backwards in order to minimize any bias resulting from selective placement with in each sub plot for grass species samples collection. Then, all the above ground forage samples were cut by using cutter and collected in paper bag. The fresh weight of forage sample was measured in the field with a scale and taken to Yaballo Pastoral and Dryland Agriculture Research Center soil laboratory and oven dried for 24 h at 105 °C to determine the dry biomass. Then, the dry matter was measured after 24 h drying and converted into kilograms per hectare (kg/ ha). Data collection on grass species sampling was done twice per year (during dry and wet season).
Determining the linkage between forage biomass and NDVI value
In order to determine the linkage between the forage biomass and the NDVI value, the average NDVI values were derived from plot-specific extractions. The extracted plot-specific NDVI values were matched with the plot-specific forage biomass quantity for each land cover type monitored [60].
Socio-demographic profile of the respondents
The Social-demographic status (age, sex, education level and income source) of the respondents was analyzed using Microsoft excel and descriptive statistics in the Statistical Package for Social Sciences (SPSS). The spatial and temporal trends in increasing number of agro-pastoralists, the drivers of rangeland vegetation cover and forage production change, the infestation rate of shrub plant species, the expansion agricultural lands, and rangeland indigenous management methods were analyzed using descriptive statistics.
